Herpes simplex virus (HSV) keratitis, particularly disease affecting the corneal stroma, is a leading cause of visual impairment. Our studies have implicated the cytotoxic T lymphocyte (CTL) response to HSV-1 in the pathogenesis of stromal disease, and demonstrated the feasibility of an immunoregulatory approach to prevent corneal scarring. If one can identify functional T cells that are protective or destructive in the cornea, and the HSV-1 antigens that regulate their activity, it should be possible to develop subunit vaccines and passive immunization procedures that will protect the cornea without the opacification and scarring that results in visual morbidity. The long range goals of this research program are: (a) to define the roles of functionally distinct T lymphocyte populations in the protective and immunopathologic reactions to HSV in the cornea, (b) to gain a detailed understanding of the HSV-1 antigens that activate these lymphocytes, and (c) to eventually apply this information to the development of agents that augment the immunological protection of the cornea without the associated immunopathology. Two major groups of experiments are proposed to accomplish these goals. First, the participation of specific types of T lymphocytes in protective and immunopathologic protection of the cornea without the associated immunopathology. Two major groups of experiments are proposed to accomplish these goals. First, the participation of specific types of T lymphocytes in protective and immunopathologic reactions to HSV-1 in the cornea will be investigated. Mice will be depleted of the CD-4 or CD-8 T lymphocyte subpopulations, or all T-cells, through administration of monoclonal antibodies specific for L3T4, Lyt-2, or Thy-1 differentiation markers respectively. The corneas of the T cell- depleted mice will be infected with HSV-1, and the development of corneal disease monitored. The immune response will also be monitored both in the lymphoid organs and in the infected corneas of these depleted mice. These studies will identify associations between distinct patterns of immune response and corneal disease. The depletion studies will be complemented by experiments in which mice that have been depleted of specific T lymphocyte populations will be reconstituted with HSV-specific cloned T lymphocytes of the depleted type. The role that each functionally distinct cloned T lymphocyte plays in the development of corneal disease will be directly demonstrated. The second set of experiments examines, at the epitope level, the roles of individual HSV-1 antigens for stimulating or suppressing specific types of immune responses. These experiments will also determine how many class I or class II major histocompatibility complex (MHC) molecules restrict recognition of each epitope, as an indication of the scope of the T-cell repertoire that might be activated by that epitope. Strains of HSV-1 with deletion or point mutations affecting the major HSV-1 cell surface glycoproteins, as well as truncated proteins and we will use peptide fragments to identify the antigens recognized by functionally distinct HSV- specific T-cells. These proteins and peptides will be presented to the T lymphocytes in the context of specific class I and class II molecules to determine their MHC restriction patterns. having identified the HSV epitopes recognized by the T lymphocytes which play a protective or an immunopathologic role in the cornea, peptide fragments containing these epitopes will be used to modulate the immune response to HSV-1 in vivo. Attempts will be made to identify the appropriate mixture of peptides to augment protective immunity while suppressing immunopathologic responses. These proposed studies may ultimately lead to immunology-based therapy for HSV corneal disease, and to the development of a subunit vaccine against ocular HSV infections.